What we're seeing here are two solid-state Tesla Coils, each running in the 41 kHz range, performing a little concert thanks to some ingenious electrical work. The coils, which have been nicknamed the Zeusaphone, were developed by Tesla enthusiasts Jeff Larson and Steve Ward.
On his site, Larson explains that a particular version of this type of coil can be good for audio modulation because it produces several hundred sparks per second. The apparently continuous crack of light we see is actually a series of brief sparks. Larson and Ward figured out a way to modulate this frequency digitally, and get the sparks to crank out the sound waves or musical notes they want.
This concert features "Dance of the Sugarplum Fairies," but they've also done the theme from Super Mario Brothers and others. In terms of audio quality it doesn't quite measure up, but when you're talking pure spectacle, this has to be tops. You wonder if Tesla himself would be proud.—Gregory Mone